Blue Origin thread.

[tater]

4 minutes ago, sevenperforce said:

Al grid fins used to get melty during ultra-high-velocity heavy-payload GTO missions with no boostback burn, where ASDS was maximally downrange. RTLS wouldn't have been possible under those circumstances.

Yes.

What I read was that ASDS landings were better on the boosters, not that some ASDS landings were better on the boosters. If the statement is that ASDS is better on the boosters for missions with enough margin to RTLS anyway (or something close to that), then I agree, it's all about propellants, since they have more reserve with no boost back, obviously.

On missions where they must use ASDS, I think it's not at all clear that ASDS is more gentle on them.

Edited May 1, 2018 by tater

[sevenperforce]

47 minutes ago, tater said:

What I read was that ASDS landings were better on the boosters, not that some ASDS landings were better on the boosters. If the statement is that ASDS is better on the boosters for missions with enough margin to RTLS anyway (or something close to that), then I agree, it's all about propellants, since they have more reserve with no boost back, obviously.

On missions where they must use ASDS, I think it's not at all clear that ASDS is more gentle on them.

Can't imagine it would be. Those octawebs get torched AF on the heavyweight GTO missions.

[tater]

If boostback depletes prop reserves enough that there is a significant degradation of boosters, then I would expect to see more voluntary ASDS landings for block 5, even when margins exist for RTLS. Presumably this is why, in addition to FH, they are making another ASDS. If they head to more ASDS landings, logistics will become more complex as well (a week in transit with the booster aboard).

I wonder if what are now "extreme" ASDS recoveries are simply abandoned in favor of FH...

On topic: If prop reserves are the special sauce to many reuses, then BO has the right idea.

Edited May 1, 2018 by tater

[sevenperforce]

10 minutes ago, tater said:

If boostback depletes prop reserves enough that there is a significant degradation of boosters, then I would expect to see more voluntary ASDS landings for block 5, even when margins exist for RTLS. Presumably this is why, in addition to FH, they are making another ASDS. If they head to more ASDS landings, logistics will become more complex as well (a week in transit with the booster aboard).

I wonder if what are now "extreme" ASDS recoveries are simply abandoned in favor of FH...

On topic: If prop reserves are the special sauce to many reuses, then BO has the right idea.

Which is a great segue back to BO.

Can anyone confirm that the BE-4's ignition system is TEA-TEB just like the Merlin's? I seem to recall seeing a green flash at the start of all the BE-4 fire tests.

The NG first stage will likely have a much poorer mass ratio than a Falcon 9, so perhaps 1/7 of rated thrust is enough for a hover.

Raptor will use spark ignition eventually. 

[MaverickSawyer]

Dunno about TEAl/TEB. Could be a lighting bug with the camera as the exhaust flames saturate the CCD chip momentarily.

[sevenperforce]

12 minutes ago, MaverickSawyer said:

Dunno about TEAl/TEB. Could be a lighting bug with the camera as the exhaust flames saturate the CCD chip momentarily.

I guess...well, what ELSE would they be using for ignition?

[Brotoro]

1 hour ago, tater said:

Yes.

What I read was that ASDS landings were better on the boosters, not that some ASDS landings were better on the boosters. If the statement is that ASDS is better on the boosters for missions with enough margin to RTLS anyway (or something close to that), then I agree, it's all about propellants, since they have more reserve with no boost back, obviously.

On missions where they must use ASDS, I think it's not at all clear that ASDS is more gentle on them.

Possibly the greater stress on the booster during a RTLS comes from getting blasted side-on by the exhaust of the upper stage engine while doing the quick flip for boostback.

[sevenperforce]

19 minutes ago, Brotoro said:

Possibly the greater stress on the booster during a RTLS comes from getting blasted side-on by the exhaust of the upper stage engine while doing the quick flip for boostback.

Peak exhaust impingement on the first stage at MVac ignition is the same whether the booster is flipping or not. By the time the booster is sideways during a boostback flip, the MVac is already far enough away that impingement is essentially nil.

Plus, boostback happens for many ASDS landings as well.

[mikegarrison]

2 hours ago, sevenperforce said:

I guess...well, what ELSE would they be using for ignition?

Lots of ways to ignite a fire. Most jet engines don't use a chemical starter like TEA/TEB. Instead they use electrical ignitors.

[sevenperforce]

4 minutes ago, mikegarrison said:

Lots of ways to ignite a fire. Most jet engines don't use a chemical starter like TEA/TEB. Instead they use electrical ignitors.

Right, that's what's planned for Raptor as well, but the test Raptors use TEA/TEB:

Spoiler

 

You can't use spark ignition for kerolox engines but it works great for hydrolox engines and should work well enough for methalox...or, at least, full-flow staged-combustion methalox. I don't know if it will work for ORSC.

[mikegarrison]

40 minutes ago, sevenperforce said:

You can't use spark ignition for kerolox engines

Why not? As I said, that's what is used for jet engines that burn kerosene. I haven't looked into rocket engine ignition in any detail, but there is nothing about kerosene per say that makes it impossible to ignite with an electrical ignitor.

[SuperFastJellyfish]

https://blogs.nasa.gov/J2X/tag/ignition/

Your guys' convo led me to this interesting blog about liquid rocket ignition. 

[sevenperforce]

1 hour ago, mikegarrison said:

Why not? As I said, that's what is used for jet engines that burn kerosene. I haven't looked into rocket engine ignition in any detail, but there is nothing about kerosene per say that makes it impossible to ignite with an electrical ignitor.

Spark ignition in rocket engines is much trickier than in jets or ICEs; your propellant must be vaporized (not just aerosolized) and you usually have to ignite a small amount and then use that as a torch to light the main body of propellant at exactly the right time without any destructive interference or wave collisions. 

[Wjolcz]

So BE-4 will be metholox? I thought initially it was going to be hydrolox? And they are meant to be on Vulcan, right? How will that affect Vulcan? Or are they making 2 variants?

Btw, can a hydrolox engine be fuelled by methane without much/any redesign?

[tater]

Be-4 has always been exclusively methlox. Vulcan would be methlox.

Be-3 has always been exclusively hydrolox.

 

[kerbiloid]

5 hours ago, Wjolcz said:

Btw, can a hydrolox engine be fuelled by methane without much/any redesign?

+1 to this question.

As we know, RD-701 has sea-level kerohydrolox mode and vacuum purehydrolox mode, and switches from the former to the latter right in flight.
As kerosene is even farther from hydrogen than methane, probably methalox/hydrolox thing is also possible.

Though, there is a circumstance. In both modes RD-701 is being cooled by LH2 flow.
Not sure if methane could be used for that in the same pipes, with same efficiency.
(Because hydrogen heat capacity is outstanding, so the cooling pipes are designed for this specific agent, and can be too puny for any other).

So maybe it should be limited with methahydrolox vs purehydrolox modes, requiring hydrogen usage at least for cooling.

Btw, which component cools BE-4 ?

Edited May 2, 2018 by kerbiloid

[mikegarrison]

2 hours ago, kerbiloid said:

+1 to this question.

As we know, RD-701 has sea-level kerohydrolox mode and vacuum purehydrolox mode, and switches from the former to the latter right in flight.
As kerosene is even farther from hydrogen than methane, probably methalox/hydrolox thing is also possible.

Though, there is a circumstance. In both modes RD-701 is being cooled by LH2 flow.
Not sure if methane could be used for that in the same pipes, with same efficiency.
(Because hydrogen heat capacity is outstanding, so the cooling pipes are designed for this specific agent, and can be too puny for any other).

So maybe it should be limited with methahydrolox vs purehydrolox modes, requiring hydrogen usage at least for cooling.

Btw, which component cools BE-4 ?

We also know that it is a low TRL engine that has never flown.

[kerbiloid]

Just now, mikegarrison said:

We also know that it is a low TRL engine that has never flown.

As well as Raptor, Vulcan, etc.

The question was about methane/hydrogen possibility.

[MaverickSawyer]

7 hours ago, Wjolcz said:

Btw, can a hydrolox engine be fuelled by methane without much/any redesign?

Absolutely not. The entire engine, from propellant feed lines, to turbopumps, to regenerative cooling, to injector head, to chamber geometry... It's designed around using liquid hydrogen (which, if my understanding is correct, actually turns into a supercritical fluid during its run through the engine) and its unique mechanical and chemical properties. Throwing methane at it is a 100% guaranteed way to grenade the engine, if not upon ignition, then certainly within a second or two after startup.

Case in point: Look at the Aerojet LR-87 (Titan first stage engine). They started out kerolox, then switched to hypergolic for the later versions. They had enormous issues with combustion instability, with thrust chambers being literally sawed off just past the injector face from a standing wave of that instability burning through the chamber walls. They wound up having to completely redesign the injector plate.

That said, I seem to recall there being talk of Rocketdyne having converted an RL-10 to run metholox for developmental purposes. Dunno if there's any truth to it, but it would be a good reference point for how much work would be required.

 

13 hours ago, sevenperforce said:

I guess...well, what ELSE would they be using for ignition?

As others have mentioned, an augmented spark igniter would be my bet. No fussy hazardous chemicals to handle. Besides, they don't seem to use a chemical ignition system on BE-3, so they've probably used a variant of that system for BE-4, as it's something they're familiar with.

[kerbiloid]

3 minutes ago, MaverickSawyer said:

Absolutely not.

http://www.buran.ru/htm/rd-701.htm

Kerosene / hydrogen, even worse difference than methane / hydrogen

Again, the question is not about this particular engine (RD-701) experience, but about technical possibility of fuel switch.

Edited May 2, 2018 by kerbiloid

[mikegarrison]

5 minutes ago, kerbiloid said:

As well as Raptor, Vulcan, etc.

The question was about methane/hydrogen possibility.

Yes, true enough.

[MaverickSawyer]

20 minutes ago, kerbiloid said:

http://www.buran.ru/htm/rd-701.htm

Kerosene / hydrogen, even worse difference than methane / hydrogen

Again, the question is not about this particular engine (RD-701) experience, but about technical possibility of fuel switch.

BUT, that engine was designed from the outset to be a tripropellant engine. The question was about simply feeding an engine a new fuel with minimal modifications. RD-701 is NOT a fair comparison.

[kerbiloid]

13 minutes ago, MaverickSawyer said:

BUT, that engine was designed from the outset to be a tripropellant engine. The question was about simply feeding an engine a new fuel with minimal modifications. RD-701 is NOT a fair comparison

As I can get, the question was: can we feed the same engine without modification with methane or hydrogen in turn.

RD-701 is a sample of engine which can be, absolutely unmodified, fed by pure hydrogen or kerosene with hydrogen mixture.
It has 2x2 MN on sea level and 2x0.8 MN in vacuum, this is absolutely normal thrust for launch vehicle (though it was designed for a spaceplane).

So, as I have written, such switchable engine probably anyway requires LH2 among the components (because it's used as a cooling agent), but it can definitely consume both hydrogen and hydrocarbons.

The idea of methane usage is just to use cheaper and denser fuel than hydrogen when possible, not "or-or". 
Here we can see an implemented example of engine which can be fed mostly with hydrocarbons, using hydrogen as admixture. 
Maybe not purist enough, but does exactly what is required.

Additionally, it can switch right in the flight just due to its construction. Just combine cryotanks in required proportion.

Edited May 2, 2018 by kerbiloid

[sevenperforce]

6 hours ago, MaverickSawyer said:

As others have mentioned, an augmented spark igniter would be my bet. No fussy hazardous chemicals to handle. Besides, they don't seem to use a chemical ignition system on BE-3, so they've probably used a variant of that system for BE-4, as it's something they're familiar with.

The BE-3 uses a consumable solid-fueled igniter.

[mikegarrison]

8 hours ago, MaverickSawyer said:

As others have mentioned, an augmented spark igniter would be my bet. No fussy hazardous chemicals to handle. Besides, they don't seem to use a chemical ignition system on BE-3, so they've probably used a variant of that system for BE-4, as it's something they're familiar with.

1 hour ago, sevenperforce said:

The BE-3 uses a consumable solid-fueled igniter.

Isn't that the same thing? An electrical trigger that lights off a small solid pyro charge, thus "augmented"?